633308-89-1Relevant articles and documents
Regio- and stereoselectivity of the SiO2-catalyzed reaction of thiocamphor (=1,7,7-trimethylbicyclo[2.2.1]heptane-2-thione) with optically active monosubstituted oxiranes
Fu, Changchun,Linden, Anthony,Heimgartner, Heinz
, p. 2258 - 2271 (2007/10/03)
The reactions of the enolizable thioketone (1R,4R)-thiocamphor (= (1R,4R)-1,7,7-trimethylbicyclo[2.2.1]-heptane-2-thione; 1) with (S)-2-methyloxirane (2) in the presence of a Lewis acid such as SnCl4 or SiO2 in anhydrous CH2Cl2 led to two diastereoisomeric spirocyclic 1,3-oxathiolanes 3 and 4 with the Me group at C(5′), as well as the isomeric β-hydroxy thioether 5 (Scheme 2). The analogous reactions of 1 with (RS)-, (R)-, and (S)-2-phenyloxirane (7) yielded two isomeric spirocyclic 1,3-oxathiolanes 8 and 9 with Ph at C(4′), an additional isomer 13 bearing the Ph group at C(5′), and three isomeric β-hydroxy thioethers 10, 11, and 12 (Scheme 4). In the presence of HCI, the β-hydroxy thioethers 5, 10, 11, and 12 isomerized to the corresponding 1,3-oxathiolanes 3 and 4 (Scheme 3), and 8, 9, and 13, respectively (Scheme 5). Under similar conditions, an epimerization of 3, 8, and 9 occurred to yield the corresponding diastereoisomers 4, 14, and 15, respectively (Schemes 3 and 6). The structures of 9 and 15 were confirmed by X-ray crystallography (Figs. 1 and 2). These results show that the Lewis acid-catalyzed addition of oxiranes to enolizable thioketones proceeds with high regio- and stereoselectivity via an SN2-type mechanism.
